JP2011100665A - Binder resin composition for electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a binder resin composition for lithium-ion battery electrodes that has strong adhesiveness and is expected to improve Li-ion conduction by the presence of many structures of vinyl cyanide monomer units and a slight amount of copolymerizing monomer components, containing a carboxylic acid, in a binder resin containing the structures of vinyl cyanide monomer units. <P>SOLUTION: A binder composition for a lithium-ion battery is configured as follows. In a binder resin composition containing a single resin or two or more kinds of resins, a vinyl cyanide monomer is 85.0-94.0 mol% and a vinyl monomer unit containing a carboxyl group is 0.001-0.080 mol% respectively based on 100 mol% of the total monomer units in the composition. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a binder resin composition for battery electrodes, an electrode for lithium ion batteries, and a battery.

  Rechargeable batteries are expected to further expand the battery market for use in weak consumer applications such as notebook computers and mobile phones, and recently as storage areas for hybrid and electric vehicles. As secondary batteries used for these power sources, lithium ion secondary batteries (hereinafter sometimes simply referred to as batteries) have been frequently used. In weak consumer applications, miniaturization, thinning, lightening, and high performance are rapidly progressing. Fluorine-containing polymers such as polyvinylidene fluoride are widely used as battery binders, but it has been difficult to increase battery capacity and improve rate characteristics due to insufficient binding power. As a method to remedy this drawback, it is proposed to use a polyacrylonitrile-based (hereinafter sometimes referred to as “PAN-based”) resin having oxidation-reduction resistance comparable to PVDF as a binder and introduce a carboxyl group into the resin. (See Patent Document 1). Although the binding property has been improved, since Li ions are strongly bound to the carboxyl group, there is a problem that the mobility of lithium ions is lowered and the ionic conductivity in the vicinity of the active material is lowered. Therefore, it is required to reduce the amount of carboxyl groups as much as possible while maintaining the adhesive property of the current collector.

  In the prior art (Patent Documents 1 to 3), a carboxyl group is introduced into a binder using a PAN-based resin, and contains a high proportion of acrylonitrile monomer units of 85 mol% or more, and the carboxyl in the binder. There has been no report of an example in which the binder resin composition in which the group is present in an extremely small amount of 0.08 mol% or less is firmly adhered to the current collector.

Registration 431002 Tokushui WO06 / 033173 Special table 2008-546135

  An object of the present invention is to provide a binder resin containing a vinyl cyanide monomer unit structure in which a large amount of vinyl cyanide monomer unit structure is present and a small amount of a comonomer component containing a carboxylic acid is used. An object of the present invention is to provide a binder resin composition for strongly adhesive lithium ion battery electrodes that is expected to improve the conduction of Li ions.

The gist of the invention is that, in a binder resin composition containing one or more resins alone, the vinyl cyanide monomer in 100 mol% of the total monomer units of the composition is 85.0 mol% to 94.0 mol. %, A vinyl monomer unit containing a carboxyl group is 0.001 mol% to 0.080 mol%, a binder composition for a lithium ion battery.
The second gist is an electrode for a lithium ion battery comprising a mixture layer containing the binder composition and a current collector.
The third gist is a battery for a lithium ion battery including the battery electrode.

  The binder resin of the present invention can provide a binder resin composition excellent in adhesiveness to a current collector while most of the structure is an electrochemically stable vinyl cyanide monomer unit structure.

  The binder resin composition for a lithium battery electrode includes a copolymer containing a vinyl cyanide monomer unit and a vinyl monomer unit containing a carboxyl group.

  The vinyl cyanide monomer is not particularly limited, and examples thereof include vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, α-cyanoacrylate, dicyanovinylidene, and fumaronitrile. Among these, acrylonitrile is preferable from the viewpoint of ease of polymerization and cost performance. These vinyl cyanide monomers are used alone or in combination of two or more. It is preferable that acrylonitrile is contained, for example, in an amount of 85 to 94 mol% with respect to the total amount of the vinyl cyanide monomer.

  The monomer containing a carboxyl group is not particularly limited, and examples thereof include acrylic carboxyl group-containing monomers such as acrylic acid and methacrylic acid, croton carboxyl group-containing monomers such as crotonic acid, maleic acid, and the like. Maleic carboxyl group-containing monomers such as acids and anhydrides, itaconic carboxyl group-containing monomers such as itaconic acid and anhydrides, and citraconic carboxyl group-containing monomers such as citraconic acid and anhydrides thereof Examples include masses. Among these, acrylic acid is preferable from the viewpoints of ease of polymerization, cost performance, flexibility and flexibility of the electrode, and the like. These carboxyl group-containing monomers are used alone or in combination of two or more. It is desirable that the carboxyl group-containing monomer is 0.001 mol% to 0.080 mol%, preferably 0.01 mol% to 0.07 mol%.

  The binder resin composition can also contain other monomers different from the vinyl cyanide monomer or the carboxyl group-containing monomer. Other monomers are not particularly limited. For example, (meth) acryl such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, and the like. Acid esters, vinyl halides such as vinyl chloride, vinyl bromide, vinylidene chloride, acids such as (meth) acrylic acid, itaconic acid, crotonic acid and their salts, maleic imide, phenylmaleimide, (meth) acrylamide , Styrene, α-methylstyrene, vinyl acetate, sodium (meth) allylsulfonate, sodium (meth) allyloxybenzenesulfonate, sodium styrenesulfonate, 2-acrylamido-2-methylpropanesulfonic acid and salts thereof It is done. These other monomers can be used alone or in combination of two or more.

Regardless of the mode of the binder resin composition, as a method for introducing a carboxyl group-containing monomer into a cyanide monomer unit, copolymerization of both unit monomers and blending of a resin containing each monomer unit Can be mentioned.
The polymerization mode for obtaining the resin is not particularly limited, such as bulk polymerization, suspension polymerization, emulsion polymerization, solution polymerization, etc., but it is easy to synthesize the resin, easy to perform post-treatment such as recovery and purification, etc. And suspension polymerization in water is preferred.

  As a polymerization initiator for carrying out suspension polymerization in water, a water-soluble type is preferable from the viewpoint of polymerization initiation efficiency and the like. Examples of the water-soluble polymerization initiator include persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate, water-soluble peroxides such as hydrogen peroxide, 2,2′-azobis (2-methylpropionamidine hydro Water-soluble azo compounds such as chloride), oxidizing agents such as persulfates, reducing agents such as sodium hydrogen sulfite, ammonium hydrogen sulfite, sodium thiosulfate, hydrosulfite, and polymerization accelerators such as sulfuric acid, iron sulfate, and copper sulfate. A combined redox type (redox type) and the like can be mentioned. Among these, persulfates are preferable in terms of ease of resin synthesis.

  Further, when carrying out suspension polymerization in water, a chain transfer agent can be used for the purpose of adjusting the molecular weight. Examples of the chain transfer agent include mercaptan compounds, thioglycol, carbon tetrachloride, α-methylstyrene dimer, and the like. Among these, α-methylstyrene dimer is preferable from the viewpoint of low odor.

  Furthermore, when carrying out suspension polymerization in water, a solvent other than water can be added as required, such as adjustment of the suspended particle diameter. Examples of solvents other than water include amides such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, and N, N-dimethylformamide, N, N-dimethylethyleneurea, and N, N-dimethylpropyleneurea. , Ureas such as tetramethylurea, lactones such as γ-butyrolactone, γ-caprolactone, carbonates such as propylene carbonate, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate, ethyl acetate, n acetate -Esters such as butyl, butyl cellosolve acetate, butyl carbitol acetate, ethyl cellosolve acetate and ethyl carbitol acetate, glymes such as diglyme, triglyme and tetraglyme, toluene, xylene and cyclohexane And the like, sulfoxides such as dimethyl sulfoxide, sulfones such as sulfolane, alcohols such as methanol, isopropanol, and n-butanol. These solvents can be used alone or in combination of two or more.

  The binder resin composition of the present invention can be used in combination with a binder that improves battery performance and an additive such as a viscosity modifier or a fluidizing agent that improves the coating properties of the battery electrode slurry. These additives include cellulosic polymers such as styrene-butadiene rubber, carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, ammonium salts thereof, alkali metal salts, and poly (meth) acrylic acid such as sodium poly (meth) acrylate. Salt, polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, acrylic acid or copolymer of acrylate and vinyl alcohol, maleic anhydride or copolymer of maleic acid or fumaric acid and vinyl alcohol, modified polyvinyl alcohol, modified polyacrylic acid , Polyethylene glycol, polycarboxylic acid, polyacrylonitrile, polymethacrylonitrile, ethylene-vinyl alcohol copolymer, vinyl acetate polymer; Oraido, tetrafluoroethylene, fluorine-based polymers such as hexafluoropropylene; and the like. The use ratio of these additives can be freely selected as necessary. Also, these polymers need not be in the form of particles in the binder composition. Among these, as for the additive finally remaining on the electrode, it is particularly preferable to use an electrochemically stable additive. The binder resin composition is usually stored in the form of a powder or a dope dissolved or dispersed in a solvent.

  The mixture layer refers to a phase including an active material and a binder resin composition in an electrode. Generally, it is a solid phase formed by applying a slurry obtained by dissolving or dispersing an active material and a binder resin composition in a solvent on a foil and drying it.

  Any active material may be used as long as the potential of the positive electrode material is different from that of the negative electrode material. For example, in the case of a lithium ion battery, the voltage is about 4 V by using Li-containing composite oxide for the positive electrode and graphite for the negative electrode. In the case of a lithium ion battery, as the negative electrode active material, for example, a carbon material such as graphite, amorphous carbon, carbon fiber, coke, activated carbon or the like is preferable. Such a carbon material and a metal such as silicon, tin, silver, or the like Composites with these oxides can also be used.

On the other hand, as the positive electrode active material, for example, a lithium-containing metal composite oxide containing at least one metal selected from lithium and iron, cobalt, nickel, and manganese is preferable. These active materials are used alone or in combination of two or more.
Note that the positive electrode active material may be used in combination with a conductive additive. Examples of the conductive assistant include graphite, carbon black, acetylene black, and the like. These conductive assistants may be used alone or in combination of two or more.

  There is no restriction | limiting in particular as a solvent used for manufacture of a mixture layer, What is necessary is just a solvent which can melt | dissolve or disperse | distribute a binder composition uniformly. As this solvent, the solvent used when preparing the dope by dissolving the binder resin composition is used as it is. For example, various solvents such as water and organic solvents can be used. For example, N-methyl-2-pyrrolidone and N-methyl-2-pyrrolidone and ester solvents (ethyl acetate, n-butyl acetate, butyl cellosolve acetate, butyl carbitol acetate, etc.) or glyme solvents (diglyme, triglyme, tetraglyme) Etc.) is preferred. These solvents may be used alone or in combination of two or more. The amount of the solvent used is not particularly limited as long as the binder resin composition is at least a necessary minimum amount capable of maintaining a dissolved or dispersed state at room temperature, but in the slurry preparation step in the subsequent lithium ion battery electrode preparation, Usually, in order to adjust the viscosity while adding a solvent, it is preferable to use an arbitrary amount that is not excessively diluted.

  The current collector may be any material having conductivity, and for example, a metal can be used. More specifically, aluminum, copper, nickel, etc. can be used as the metal. Further, the shape of the current collector is not particularly limited, but a thin film is preferable. The thickness of the current collector is, for example, 5 to 30 μm, preferably 8 to 25 μm. The shape of the current collector includes, for example, a net shape and a fiber shape, and is not limited to a thin film shape.

  The electrode of the present invention can be produced without any particular limitation using a known electrode production method. For example, a slurry containing the binder resin composition, a solvent, and an active material is applied to a current collector, Subsequently, it can manufacture by removing a solvent and rolling as needed and forming a mixture layer in the collector surface. Here, application | coating can be performed using a comma coater etc., for example.

  Although there is no restriction | limiting in particular about the manufacturing method of the battery of the said invention, All can use a well-known method. In the case of a lithium ion battery, for example, first, two electrodes, a positive electrode and a negative electrode, are wound through a separator made of a polyethylene microporous film. The obtained spiral wound group is inserted into a battery can, and a tab terminal previously welded to a negative electrode current collector is welded to the bottom of the battery can. Inject the electrolyte into the resulting battery can, weld the tab terminal that was previously welded to the positive electrode current collector to the battery lid, and place the lid on the top of the battery can via an insulating gasket A battery is obtained by caulking and sealing the part where the lid and the battery can are in contact.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited by these.
Resins having the compositions shown in the table below were prepared. The unit is% by weight.

<Preparation of binder resin composition>
Resin A-1 was dissolved in N-methyl-pyrrolidone to prepare a 10 wt% dope. Resin B-1 was blended so that the weight ratio of the solid content of A / B was 99/1 to 80/20.
The following table shows the amount of carboxyl group-containing monomer units per 100 moles of acrylonitrile monomer units. The values in the table indicate the value of carboxyl group-containing monomer unit amount × 100.

A test piece for evaluating the adhesiveness of the binder resin composition was prepared as follows.
The adhesion between the current collector and the binder resin composition of the present invention was evaluated as follows. A negative electrode current collector copper foil was fixed to a glass plate, and a dope was applied thereto at a thickness of 130 μm.
A carbon fiber (CF) non-woven fabric (thickness 60 μm, laboratory product) was placed on the coated portion, and was well blended with the dope, and dried at 100 ° C. for 1 hour. The sheet was cut into a width of 1 cm, the CF sheet side of the obtained strip-shaped piece was affixed to a plastic plate with a double-sided tape, and pressure-bonded with a rubber roller was used as a test piece. When the Cu foil portion is pulled in the 180 ° direction, peeling occurs at the interface between the CF nonwoven fabric and the Cu foil.

The adhesion evaluation was performed as follows.
<Hand peel test>
The copper foil of the test piece was peeled by hand in the 180 ° direction, and the peel strength was examined and evaluated in three stages.
1 point: No resistance when peeling.
2 points: There is resistance when peeling. (There is no resin remaining on the peeled surface of the Cu foil.)
3 points: There is considerable resistance when peeling. (There is a resin component on the peeled surface of the Cu foil.)
In order to compare the peel strength between the test pieces of each sample, + (plus) and-(minus) were added after the number. The following table shows the peel test results. Examples 5 to 12 show that the adhesion is sufficiently maintained even when the blend ratio is low.

<180 degree peel test with tensile and compression tester>
Evaluation was made by measuring the stress when a plastic substrate was fixed to a tensile and compression tester and the copper foil was peeled at 180 mm in a direction of 10 mm / min. The measurement range to be recorded was a portion where the CF sheet was peeled off from the copper foil side and adhered to the entire tape side in the peeling process. The average value of the values reproduced three times on the curve in the vicinity of the value that could be the lowest in that range was taken as the adhesive strength. The larger this value, the higher the adhesive strength, indicating that the binder is less likely to peel from the current collector. The following table shows the peel test results. The unit is N / cm. Examples 5-12 showed peel strength higher than a comparative example. Thus, it was revealed that the adhesiveness was sufficiently maintained even when the blend ratio was low.

Claims (3)

In the binder resin composition containing one or more resins alone, the vinyl cyanide monomer in the total monomer unit 100 mol% of the composition is 85.0 mol% to 94.0 mol%, the carboxyl group is A binder composition for a lithium ion battery, wherein the vinyl monomer unit contained is 0.001 mol% to 0.080 mol%. An electrode for a lithium ion battery comprising a mixture layer containing the binder composition and a current collector. A battery for a lithium ion battery comprising the battery electrode.